背景：我需要能够以“禁用”外观创建图像。通常建议的方法是将图像转换为灰度并显示灰度图像。缺点是它仅适用于图像，因此在您无法立即访问处于禁用状态的图像时显示图形很麻烦。现在我认为这可以使用 java.awt.Composite 即时完成（然后我不需要知道如何实现图标以使其禁用）。只有似乎没有转换为灰度的实现，所以我不得不创建自己的......
也就是说，我拼凑了一个实现（它呈现了我所期望的）。但我不确定它是否真的适用于所有情况（对于如此复杂的操作，Composite/CompositeContext 的 Javadocs 似乎非常薄）。正如您从我的实现中看到的那样，我采用一种迂回的方式逐个像素地处理，因为似乎没有简单的方法可以以不由相关栅格规定的格式批量读取/写入像素。
欢迎任何指向更广泛的文档/示例/提示的指针。
这是 SSCCE - 它通过 DisabledComposite 渲染（彩色）GradientPaint 以将渐变转换为灰度。请注意，在现实世界中，您将不知道调用了什么渲染了什么。渐变实际上只是一个示例（抱歉，但人们经常不明白这一点，所以这次我会明确说明）。
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Composite;
import java.awt.CompositeContext;
import java.awt.Dimension;
import java.awt.GradientPaint;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.image.ColorModel;
import java.awt.image.Raster;
import java.awt.image.WritableRaster;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.SwingUtilities;
public class CompositeSSCE implements Runnable {
static class DisabledComposite implements Composite {
@Override
public CompositeContext createContext(
final ColorModel srcColorModel,
final ColorModel dstColorModel,
final RenderingHints hints) {
return new DisabledCompositeContext(srcColorModel, dstColorModel);
}
}
static class DisabledCompositeContext implements CompositeContext {
private final ColorModel srcCM;
private final ColorModel dstCM;
final static int PRECBITS = 22;
final static int WEIGHT_R = (int) ((1 << PRECBITS) * 0.299);
final static int WEIGHT_G = (int) ((1 << PRECBITS) * 0.578);
final static int WEIGHT_B = (int) ((1 << PRECBITS) * 0.114);
final static int SRCALPHA = (int) ((1 << PRECBITS) * 0.667);
DisabledCompositeContext(final ColorModel srcCM, final ColorModel dstCM) {
this.srcCM = srcCM;
this.dstCM = dstCM;
}
public void compose(final Raster src, final Raster dstIn, final WritableRaster dstOut) {
final int w = Math.min(src.getWidth(), dstIn.getWidth());
final int h = Math.min(src.getHeight(), dstIn.getHeight());
for (int y = 0; y < h; ++y) {
for (int x = 0; x < w; ++x) {
int rgb1 = srcCM.getRGB(src.getDataElements(x, y, null));
int a1 = ((rgb1 >>> 24) * SRCALPHA) >> PRECBITS;
int gray = (
((rgb1 >> 16) & 0xFF) * WEIGHT_R +
((rgb1 >> 8) & 0xFF) * WEIGHT_G +
((rgb1 ) & 0xFF) * WEIGHT_B
) >> PRECBITS;
int rgb2 = dstCM.getRGB(dstIn.getDataElements(x, y, null));
int a2 = rgb2 >>> 24;
int r2 = (rgb2 >> 16) & 0xFF;
int g2 = (rgb2 >> 8) & 0xFF;
int b2 = (rgb2 ) & 0xFF;
// mix the two pixels
gray = gray * a1 / 255;
final int ta = a2 * (255 - a1);
r2 = gray + (r2 * ta / (255*255));
g2 = gray + (g2 * ta / (255*255));
b2 = gray + (b2 * ta / (255*255));
a2 = a1 + (ta / 255);
rgb2 = (a2 << 24) | (r2 << 16) | (g2 << 8) | b2;
Object data = dstCM.getDataElements(rgb2, null);
dstOut.setDataElements(x, y, data);
}
}
}
@Override
public void dispose() {
// nothing for this implementation
}
}
// from here on out its only the fluff to make this a runnable example
public static void main(String[] argv) {
Runnable r = new CompositeSSCE();
SwingUtilities.invokeLater(r);
}
// simple component to use composite to render
static class DemoComponent extends JComponent {
// demonstrate rendering an icon in grayscale with the composite
protected void paintComponent(Graphics g) {
Graphics2D g2d = (Graphics2D) g;
GradientPaint p = new GradientPaint(0, 0, Color.GREEN, 127, 127, Color.BLUE, true);
g2d.setComposite(new DisabledComposite());
g2d.setPaint(p);
g2d.fillRect(0, 0, getWidth(), getHeight());
}
}
// Fluff to use the Composite in Swing
public void run() {
try {
JFrame f = new JFrame("Test grayscale composite");
DemoComponent c = new DemoComponent();
c.setPreferredSize(new Dimension(500, 300));
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setLayout(new BorderLayout());
f.add(c, BorderLayout.CENTER);
f.pack();
f.setVisible(true);
} catch (Exception e) {
throw new RuntimeException(e);
}
}
}